This invention relates to a control system for a variable speed water turbine generator apparatus.
A water turbine generator apparatus, conventionally well known and adopted, uses a synchronous machine as a generator and therefore the frequency of generation output has a proportional relationship with the rotation number of the generator. Conversely, in a variable speed generator, the rotation number can be controlled to a value which is separate from and independent of the frequency of generation output and so, the rotation number of a water turbine can advantageously be controlled to a value at which efficiency of the water turbine is maximized while maintaining the generation output frequency at a frequency of an electric power system.
A control system for this type of variable speed water turbine generator apparatus, such as illustrated in FIG. 1 of the present application, has been proposed in, for example, JP-A-57-182920.
Referring to FIG. 1, a wound-rotor induction generator 1 is driven for rotation by means of a water turbine 2 directly connected to the rotor of the generator. The generator 1 is driven at variable speeds while a secondary winding 1b of the generator 1 being supplied with an AC exciting current which is so adjusted, by means of a cyclo-converter 3, as to have a predetermined internal phase difference angle in accordance with a rotation speed of the generator 1, so that AC power of a constant frequency equal to a rated frequency of an electric power system 4 may be generated from a primary winding 1a of the generator 1. A water turbine characteristic function generator 5 is supplied with a rotation speed signal N, a generation output command Po applied externally and a water-level detection signal H and generates an optimum rotation speed command Na and an optimum guide vane opening command Ya which are used for operating the generator apparatus at maximum efficiency. An induction machine 7 for slip phase detection has a rotor directly coupled to the generator 1 and a primary winding 7a connected to the output of the generator 1 and it delivers a slip phase signal Sp through a secondary winding 7b. The slip phase signal Sp and optimum rotation speed command Na are applied to a control unit (not shown) included in the cyclo-converter 3 in order for the cycloconverter 3 to control the frequency and internal phase difference angle of the AC exciting current supplied to the secondary winding 1b of the generator 1, in the manner described above. The optimum guide vane opening command Ya is applied to a guide vane driver 8 which in turn controls the opening of guide vanes 9 such that a waterwheel output P.sub.T can be optimized.
In the variable water turbine generator apparatus, it is required that the generation output be rendered coincident to a generation output command issued from, far example, a central load-dispatching office, and the rotation speed of the water turbine and the guide vane opening be controlled to proper values under that generation output, whereby the water turbine can be operated at maximum efficiency under that generation output. To this end, two operation terminals are adjustable which are represented by the cyclo-converter 3 operative to effect excitation control, such as frequency and internal phase difference angle control, for the rotor and by the guide vane operating of the water wheel. Importantly, it should therefore be decided what control items are to be shared by respective operation terminals in realizing a control system. The known reference, however, fails to provide sufficient disclosure in this regard. Especially, where a generation output control mode is provided independently of the aforementioned optimum rotation speed control mode and optimum guide vane control mode so that three control modes are involved, the prior art has absolutely failed to clarify a way of allotting the three control modes to the two operation terminals and compatibly applying thereto those control modes in combination.
Further, in the known reference, the response speed in the rotation speed optimizing control is retarded relative to the response speed in the guide vane optimizing control to prevent the water wheel from transiently coming into a specified bad operation or running condition range. However, on the other hand, there is a possibility that the slower response speed in the rotation speed optimizing control causes the rotation speed to overshoot and transiently go beyond a predetermined permissible variable speed band. This means that the possibility of step-out is disadvantageously increased.